I got cheats to work in Mgba for the wii. It is probably the same for the switch. You have to use the pc version to create your cheats. You load your rom on Mgba on pc and then go to tools. Find your Gba cheats for GameShark or codebreaker. Just copy and paste the cheats into the codes window and then click add gameshark or codebreaker. You have to use the right one for your codes. For example if they are GameShark codes you need to hit add gameshark. Otherwise, the codes won't apply. You can double click the name to change the name of codes. Once your done adding codes, just click save. You'll need to save it as the rom name, but with .cheats extension instead of gba. Then just place cheat file in the same folder as your rom on sd card.
--------------------- MERGED ---------------------------
Whichever cheats were turned on in pc version will be automatically applied on console version of Mgba if you followed the steps above.